1. Field of the Invention
The present invention relates to an endoscope including a bending portion that operates upon the bending portion being pulled.
2. Description of the Related Art
In recent years, medical devices to be inserted into a subject, for example, endoscopes, have been widely used in a medical field. An elongated insertion portion of an endoscope is inserted into a subject, enabling, e.g., observation and/or treatment of a site to be examined inside the subject.
Here, a configuration in which an actuating member, for example, a bending portion that is bendable in a plurality of directions is provided in the insertion portion of the endoscope is publicly known.
The bending portion is capable of, in addition to enhancement in capability of forward movement of the insertion portion in a flexed part in a duct, changing an observation direction of an observation optical system provided in a distal end portion provided so as to be continuous with a distal end in a longitudinal axis direction of the insertion portion (hereinafter simply referred to as “distal end”) of the bending portion in the insertion portion.
Typically, the bending portion includes a plurality of bending pieces joined along the longitudinal axis direction of the insertion portion and is thereby bendable in, for example, four directions: upward, downward, rightward and leftward.
More specifically, the bending portion is configured so as to be bendable in any of the upward, downward, rightward and leftward directions as a result of a corresponding one of four wires, each being inserted inside the insertion portion so as to be movable forward and backward in the longitudinal axis direction and including a distal end fixed to a bending piece positioned furthest on the distal end side in the longitudinal axis direction (hereinafter simply referred to as “distal end side”) from among the plurality of bending pieces, being pulled using an operation input section of an operation portion.
Also, in the insertion portion, a flexible tube that has flexibility and is elongated in a longitudinal axis direction is provided so as to be continuous with a proximal end in a longitudinal axis direction (hereinafter simply referred to as “proximal end”) of the bending portion.
Here, Japanese Patent Application Laid-Open Publication No. 2011-120687 discloses a configuration in which four wires are respectively inserted inside four coil sheaths, each including an element wire closely wound in a helical fashion along a longitudinal axis direction, inside a flexible tube and a distal end of each coil sheath is fixed to a distal end of the flexible tube and a proximal end of each coil sheath is fixed inside an operation portion.
The respective coil sheaths guide the respective wires in such a manner that the respective wires are movable along the longitudinal axis direction without deviating in a radial direction or a circumferential direction of the flexible tube. Also, each coil sheath has a function that, upon the bending portion being bent as a result of each corresponding wire being pulled, prevents even the flexible tube from bending together with the bending portion because of compression of the relevant coil sheath in the longitudinal axis direction due to the fixation of the distal end and the proximal end.
FIG. 13 is a partial cross-sectional view illustrating a state in which a wire is inserted inside a conventional coil sheath and including a longitudinal axis direction of the wire, and FIG. 14 is a partial cross-sectional view illustrating a state in which the coil sheath in FIG. 13 is bent and the wire is thereby drawn into the coil sheath and including the longitudinal axis direction of the wire.
Upon an insertion portion being inserted into a subject, a flexible tube passively bends along a shape of the inside of the subject because of flexibility of the flexible tube. As a result of the bending of the flexible tube, a coil sheath 120 provided inside the flexible tube bends as illustrated in FIG. 14 from a linear state along a longitudinal axis direction N, which is illustrated in FIG. 13.
Here, where the coil sheath 120 bends, a wire 110 inserted inside the coil sheath 120 may be drawn into the coil sheath 120 by the amount of the bending of the coil sheath 120.
More specifically, as illustrated in FIG. 13, where L is a length in the longitudinal axis direction N of a predetermined area of the coil sheath 120 and M is a length in the longitudinal axis direction N of the wire 110 inserted inside the coil sheath 120 in the length L, as illustrated in FIG. 14, if the coil sheath 120 bends, the wire 110 may elastically deform because the wire 110 extends by the amount of M′−M.
Still more specifically, an amount of the wire 110 drawn in upon bending of the coil sheath 120 in the predetermined area L is defined by a distance a from a line connecting contact points 122 between respective parts of an element wire 121 included in the coil sheath 120 to an outer peripheral face of the element wire 121, a diameter b of the wire 110, a bending angle θ of the coil sheath 120 and a radius R of curve of a part on the inner side in the bending direction of the coil sheath 120.
This is because, since a length L′ of the part on the inner side in the bending direction of the coil sheath 120 after the coil sheath 120 bending is L′=2πR×θ/360 and the length M′ of the wire 110 after the elastic deformation is M′=2π(R+a+b/2)×θ/360, the amount of the wire 110 drawn in can be defined by M′−L′=(2π(R+a+b/2)−2πR)×θ/360=πθ(a+b/2)/180.
Also, upon the wire 110 being pulled in order to bend the bending portion, the wire 110 is brought into contact with the part on the inner side in the bending direction of the coil sheath 120.
However, when the wire 110 is elastically deformed and the coil sheath 120 is bent as illustrated in FIG. 14, frictional resistance of the wire 110 against the part on the inner side in the bending direction of coil sheath 120 sometimes becomes large compared to the case where the wire 110 is not elastically deformed and the coil sheath 120 is not bent as illustrated in FIG. 13, which results in increase in amount of strength of pulling the wire 110.